Title page for ETD etd-08222002-152733


Type of Document Master's Thesis
Author Zhao, Jun
Author's Email Address juzhao@vt.edu
URN etd-08222002-152733
Title Development of Integrated "Chip-Scale" Active Antennas for Wireless Applications
Degree Master of Science
Department Electrical and Computer Engineering
Advisory Committee
Advisor Name Title
Raman, Sanjay Committee Chair
Stutzman, Warren L. Committee Member
Sweeney, Dennis G. Committee Member
Keywords
  • Microstrip antenna
  • power amplifier
  • integrated antenna
Date of Defense 2002-07-26
Availability unrestricted
Abstract
With the rapid expansion of wireless communication services, ultra-miniature, low

cost RF microsystems operating at higher carrier frequencies (e.g. 5-6 GHz) are in

demand for various applications. Such applications include networked wireless sensor

nodes and wireless local area data networks (WLANs). Integrated microstrip antennas

coupled directly to the RF electronics, offer potential advantages of low cost,

reduced parasitics, simplified assembly and design flexibility compared to systems

based on discrete antennas. However, the size of such antennas is governed by physical

laws, and cannot be arbitrarily reduced. The critical patch antenna dimension

at resonance needs to be ~λg/2 (where λg is the guided wavelength given by λg

=λ/sqrt(er) . Several methods are available to reduce the physical size of the antenna

to enable on-chip integration. A high dielectric constant substrate reduces the guided

wavelength. Grounding one edge of the microstrip patch enables the resonant antenna

length to be further reduced to ~λg/4. However, these techniques result in degraded

antenna efficiency and bandwidth. Nonetheless, such antennas still have potential for

use in low power/short range applications.

In this work, "electrically small" (small with respect to λo) square-shaped microstrip

patch antennas, grounded on one edge by shorting posts, have been investigated. The

antenna input impedance depends on the feed position; by adjusting the feed point,

the antenna can be tuned to match a 50 Ω or other system impedance. The antennas

were designed on a GaAs substrate, with a high dielectric constant of 12.9. The size of the patch antenna is further reduced by utilizing shorted through substrate vias

along one edge. The size of the antenna is about 4.2mm × 4.2mm, which is ~1/13 of

λo at ~5.6GHz. The antennas are practical for integration on chip. Due to the size

reduction, the simulated peak gain of the antenna is only −10.2 dB ( ~3.2% radiation

efficiency). However, this may be acceptable for short-range wireless communications

and distributed sensor network applications.

Based on the above approach, integrated GaAs "chip-scale" antennas with matching power amplifiers have been designed and fabricated. Class A tuned MESFET

power amplifiers (PAs) were designed with outputs directly matched to the antenna

feed point. The antenna is fabricated on the backside of the chip through backside

patterning; the PA feeds the antenna through a backside via. The structure is then

mounted such that the antenna faces up, and is compatible with flip-chip technology.

The measurement of a 50 Ω passive (no PA) antenna indicates a gain of -12.7dB on

boresight at 5.64 GHz, consistent with the antenna size reduction. The measurement

of one active antenna (50 Ω system) shows a gain of -4.3dB on boresight at 5.80

GHz. The other version of active antenna (22.5 Ωsystem) shows a gain of -2.9 dBi

on boresight at 5.725 GHz. The active circuitry (PA) contributes an average of ~9

dB gain in the active antenna, reasonable close to the designed PA gain of 12.7dB.

The feasibility of direct integration of a PA with an on-chip antenna in a commercial

GaAs process at RF frequencies was successfully demonstrated.

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